Method and apparatus for the electrostatic sorting of granular materials



Sept. 24, 1968 R. c. M. MOREL ETAL 3,402,814

METHOD AND APPARATUS FOR THE ELECTROSTATIC SORTING OF GRANULAR MATERIALS Filed June 25, 1964 4 Sheets-Sheet 1 Fig.2

Sept. 24, 1968 R. c. M. MOREL ETAL 3,402,814

METHOD AND APPARATUS FOR THE ELECTROSTATIC SORTING OF GRANULAR MATERIALS Filed June 25, 1964 4 Sheets-Sheet 2 Fig.3

Fig.4

Sept. 24, 1968 R. c. M. MOREL ETAL 3,402,814

METHOD AND APPARATUS FOR THE ELECTROSTATIC SORTING OF GRANULAR MATERIALS Filed June 25, 1964 4 Sheets -Sheet 3 Sept. 24, 1968 c. M. MOREL ETAL 3,402,314 METHOD AND APPARATUS FOR THE ELECTROSTATIC SORTING' OF GRANULAR MATERIALS Filed June 25. 1964 4 Sheets-Sheet 4 United States Patent "ice 19 Claims. (Cl. 209-127) The present invention relates to a method for the electrostatic sorting of powderw or granular products and to apparatus for carrying out this method.

In accordance with certain types of sorting methods and apparatus proposed heretofore, a portion of the particles of material to be sorted is selectively charged to an electrical potential of one polarity, while the remaining portion is uncharged or is charged to a potential of the opposite polarity. The particles are arranged in an extended zone which includes two oppositely poled electrodes, such that the particles having a charge of the first polarity are attracted toward one of the electrodes. The selected particles are thus separated from the uncharged particles or from the particles of the opposite polarity, as the case may be, these latter particles being attracted toward the other electrode.

Prior methods and apparatus of the foregoing type have exhibited certain disadvantages. Of particular moment was the necessity for selectively charging only certain of the panicles to a potential of given polarity. Such selective charging required relatively complex equipment which was expensive and often difficult to operate. In addition, several of the sorting methods and apparatus employed heretofore were comparatively inefficient and were not effective to separate the various groups of particles with the requisite degree of accuracy for many applications.

One general object of this invention, therefore, is to provide a novel and economical method and apparatus for the electrostatic sorting of particles.

More specifically, it is an object of this invention to provide such method and apparatus in which the need for applying a potential of given polarity to only a selected portion of the particles to be sorted is eliminated.

Another object of the invention is to provide a continuous process for the electrostatic separation of particles having a particular characteristic from other particles having different characteristics.

A further object of the invention is to provide a new and improved apparatus for the electrostatic sorting of particles which is economical to manufacture and thoroughly reliable in operation.

In accordance with one illustrative embodiment of the invention, air or other fluidizing gas is directed into a container for the particles to be sorted to form a fluidized bath or bed of particles. The particles in the fluidized bed are electrically charged by conductance with an electrode to a high DC. potential. A collector member is arranged in spaced juxtaposition with the container, and an electric field is formed between the electrode and the collector. This field is effective to transfer at least some of the particles to the exposed surface of the collector. However, the collector retains only those particles which have a common characteristic different from the corresponding characteristic of the remaining particles. The particles retained by the collector are thus separated from the remaining particles.

In accordance with one feature of the invention, in several good arrangements, all of the charged particles are exposed to a DC. potential of the same polarity,

3,402,814 Patented Sept. 24, 1968 thereby avoiding the need for complex equipment to apply a potential of given polarity to only a selected portion of the particles.

In certain advantageous embodiments, the collector member is of electrically conductive material, and the DC. potential is applied between the collector and an electrode within the fluidized bed. Substantially all of the particles in the bed are charged to a potential of given polarity and are electrostatically transferred to the collector. The particles which have a comparatively high resistivity characteristic retain their charges and are transferred by the collector to a collecting station. The charges on the particles having a lower resistivity, however, are dissipated through the conductive collector and are returned to the fluidized bed.

In other embodiments, the DC. potential, rather than being applied directly across the electrode within the fluidized bed and the collector member, is connected between the electrode and one or more additional electrodes which are arranged in spaced relationship with the collector. The use of such additional electrodes provides an additional improvement in the electrostatic field between the electrode within the bed and the collector and is of particular utility in cases in which particles of different electrical conductivity are to be separated on the basis of size or weight, for example.

In accordance with several embodiments, the collector member is in the form of an endless conveyor belt which is operated to provide continuous sorting of the particles within the fluidized bed. In other cases, there is provided a plurality of collectors which are generally in the form of flat plates, rods, etc. With this arrangement, the overall efiiciency of the system is further improved.

The foregoing and other objects and advantages of the invention will appear more clearly and fully from the following description, given by way of example, of various preferred embodiments, reference being made to the accompanying drawings, in which:

FIGURE 1 is a schematic representation, with certain parts shown in vertical section, of sorting apparatus in accordance with one illustrative embodiment of the invention for carrying out the method according to the invention;

FIGURE 2 is a schematic representation in general similar to FIGURE 1 but iilustrating another illustrative embodiment of sorting apparatus adapted to carry out the method;

FIGURE 3 is a perspective view, with certain parts shown schematically and others broken away and in section, of a further illustrative apparatus for carrying out the method;

FIGURES 4 and 5 are schematic representations in general similar to FIGURE 1 but illustrating two additional illustrative embodiments;

FIGURE 6 is a perspective view of the type shown in FIGURE 3 but illustrating still another illustrative embodiment; and

FIGURES 7 and 8 are schematic representations in general similar to FIGURE 1 but showing still further illustrative embodiments.

Referring to FIGURE 1, an open tank 1 of electrically non'conductive material forms a container for the particles 2 to be sorted. The tank 1 is of rectangular cross-section and is provided with a horizontal porous wall 3 which serves as a floor for the particles. The wall 3 is arranged in spaced relationship with the bottom of the tank to form a chamber 4 therebetween. A stream of compressed air or other fluidizing gas is directed into the chamber 4 from a pipe 5. The gas passes through the porous wall 3 to bring the particles to an agitated or fluidized state and thereby forms a fluidized bed of the particles.

Spaced above the open upper portion of the tank 1 is a collector member in the form of an endless conveyor belt 6. The belt 6 is arranged for continuous movement along a closed path between two pulleys 7. Either or both of these pulleys performs a driving function to direct the belt 6 along its path at a substantially uniform rate. The lower reach 6a of the belt is in spaced juxtaposition with the tank 1 and is continuously driven along a feed path from one side of the tank to the other in the direction of the arrow F toward a collecting station. A brush 8 or other particle removing means cooperates with the belt reach 6a at the collecting station and is disposed immediately above an open receiver tank 9.

The fluidizing tank 1 is provided with an electrode 14 which is supported within the bed of particles 2 and is spaced above the porous wall 3. The electrode 14 is in the form of an electrically conductive woven wire screen and is connected by a conductor 10 to the negative terminal of an electrostatic generator 11. The generator 11 is of conventional construction and is arranged to produce a high DC. voltage which illustratively is of the order of about ninety kilovolts. The opposite terminal of the generator 11 is connected to ground and also to the conveyor belt 6 through a conductor 12 and a sliding contact or brush 13. In the embodiment illustrated in FIGURE 1, the belt 6 advantageously is of suitable sheet metal or other electrically conductive material, for purposes that will become more fully apparent hereinafter.

The particles within the fluidized bed have particular properties or characteristics, and certain of the particles have a common characteristic which is diflerent from the corresponding characteristaic of the remaining particles. As an illustration, in the FIGURE 1 embodiment some of the particles have a comparatively high resistivity characteristic, when compared with the resistivity characteristic of the other particles. Thus, the particles in the bed may comprise particles of metallic ore, for example, having relatively good electrical conductivity and also other particles of slag, dirt, carbon residue, etc., which exhibit high dielectric properties and are to be separated from the electrically conductive particles.

Substantially all of the particles 2 within the fluidized bed are electrically charged by contact with the electrode 14 to a high DC. potential of the same negative polarity. The conveyor 6, on the other hand, is at ground potential. An electric field is thereby established between the fluidized bed and the conveyor which is effective to attract all of the charged particles toward the outer surface of the lower reach 6a. As the charged particles are transferred to the conveyor, the particles having comparatively high resistivity are retained on the reach 6a by the electric field. The charge on the relatively conductive particles, on the other hand, is dissipated through the conductive material of the conveyor such that the field is not effective to hold these latter particles thereon. The conductive particles fall from the conveyor and are returned to the fluidized bed within the tank 1.

The particles of comparatively non-conductive material on the conveyor 6 are advanced along their feed path to the brush 8 at the collecting station. The brush 8 serves to remove the particles from the conveyor so that they drop into the receiver tank 9. The particles also may be removed from the conveyor by various other devices, such as a suitable charge dissipating member, for example, and are deposited within the tank 9 in an area separate from the electrically conductive particles being returned to the fluidized bed.

In addition to enabling the accurate and efficient separation of particles of material having different resistivity characteristics, the sorting apparatus of FIGURE 1 also is advantageous in cases in which it is desired to separate particles having substantially the same resistivity characteristics on the basis or size or weight. As an illustration, in cases in which it is desired to separate only the smaller and lighter particles from a mixture of particles having varied granulometry characteristics, the spacing between the upper surface of the fluidized bed 2 and the reach 60 of the conveyor belt 6 is adjusted to vary the strength of the electrostatic field between the particles and the belt 6 in accordance with the desired particle size such that only those particles which have a comparatively light weight characteristic reach the belt. The strength of the field is insulficient, however, to transfer the heavier particles to the belt, and these latter particles remain in a fluidized state within the tank 1. The lighter particles retained by the belt have a substantially non-conductive characteristic and are advanced along the reach 6a to the receiving tank 9.

In certain advantageous embodiments, the apparatus is arranged to separate the comparatively light weight particles irrespective of whether the separated particles are of electrically conductive or nonconductive material. Referring to FIGURE 2, for example, in which corresponding components have been identified by the same reference numerals, a continuously moving conveyor belt 16' of rubber or other dielectric material is arranged above the tank 1 with its lower reach 16a in spaced juxtaposition with the fluidized bed. An electrode member 17 is spaced immediately above the reach 16a and is connected to the grounded terminal of the electrostatic generator 11. The member 17 is in the form of one or more elongated rods which extend substantially entirely from one side of the tank 1 to the other.

In operation, the smaller and lighter particles of material within the fluidized bed tend to rise to a higher level than the particles having heavier characteristics. The electrostatic field between the wire mesh electrode 14 and the electrode member 17 acts on the lighter particles to bring them into contact with the reach 16a of the conveyor belt 16', and these particles are retained on the belt as it moves along its feed path toward the receiver tank 9. However, the heavier particles, irrespective of their resistivity characteristics, do not come in contact with the belt and remain within the fluidized bed. Because of the non-conductive material of the belt, even the light weight electrically conductive particles are electrostatically retained thereon during their movement toward the tank 9. The retained particles are removed from the belt by the brush 8, which preferably is maintained at ground potential, and are deposited in the tank. The apparatus is thus effective to separate particles having small size and weight characteristics from a mass of particles of varied granulometry.

Referring now to FIGURE 3, the dielectric tank 1 for the fluidized bed is positioned in spaced juxtaposition with a collector member which comprises an electrically conductive conveyor belt 36. The conveyor belt 36 and the wire mesh electrode 14 are both connected to the grounded terminal of the generator 11, while the negative terminal of the generator is connected to a plurality of auxiliary electrodes in the form of rods 37 which extend horizontally between the fluidized bed and the belt 36 and are arranged a slight distance above the upper level of the bed in spaced-apart parallel relationship with each other.

The particles of material Within the fluidized bed are charged to ground potential by contact with the electrode 14 and are attracted by the high negative potential of the rods 37. Substantially all of the particles are sufficiently accelerated by the electrostatic field to pass between the rods 37 and thus reach the belt 36. As hereinbefore described, because the belt is electrically conductive, only the particles having comparatively high resistivity characteristics adhere to the belt and are transferred to the receiving tank 9. The electrically conductive particles, on the other hand, fall back into the fluidized bed.

In cases in which the conveyor belt 36 is made of electrically nonconductive material, every charged particle coming in contact with the belt remains thereon and is conveyed toward the tank 9 in the manner hereinbefo-re described. By adjusting the height of the fluidized bed, only the lighter particles contact the belt and are separated from the heavier particles irrespective of their resistivity characteristics.

According to a modification of the apparatus shown in FIGURE 3, the conveyor belt 36 is charged to a high negative potential identical with that of the rods 37. With this arrangement, the acceleration of the particles toward the belt is further increased.

Referring to FIGURE 4, a series of spaced-apart collecting tanks 46 of U-shaped cross-section are positioned above the tank 1 containing the fluidized particles 2. Above these tanks 45 is provided an electrically conductive deflector 47 which serves as an auxiliary electrode and is of corrugated or zig-zag cross-section. The lower portions of the deflector 47 are positioned intermediate each pair of adjacent tanks 46, while the upper portions of he deflector are located above the central portions of the corresponding tanks. The tanks 46 are of electrically conductive material and are connected in series with the negative terminal of the electrostatic generator 11. The grounded terminal of this generator is connected to the electrode 14 immersed in the fluidized bed and also to the deflector 47.

In operation, the particles 2 within the fluidized bed are charged to ground potential and are attracted by the negatively charged assembly of tanks 46. At least some of the particles rise between and above the tanks 46 and rebound off the grounded deflector 47 into the tanks. The particles within the tank are thus separated from the fluidized bed and are thereafter removed from the tanks in any suitable manner.

The applications of the FIGURE 4 embodiment include the extraction of particles having comparatively light weight characteristics from particles having heavier characteristics and the extraction of the most highly charged particles from a mass of particles.

In a modification, the deflector 47 is electrically connected to the receiver tanks 46, rather than to ground, and thus is charged with the high negative potential of the latter.

In the FIGURE 5 embodiment, the tank 1 containing the fluidized bed of particles 2 is surrounded by a plurality of collector electrodes 51 which comprise a series of flat, electrically conductive plates extending horizontally around the upper edge of the tank. The charging electrode 14 within the tank is connected to the high voltage terminal of the generator 11, while the collector electrodes 51 are connected to ground, as is the opposite terminal of the generator.

The particles 2 are charged by the electrode 14 to a high DC. potential of the same polarity and are raised to a height according to the charge per unit of weight which they receive. Those particles which rise sufficiently high to pass above the sides of the tank 1 are attracted by the grounded electrodes 51 and are collected thereby. The thus collected particles are then removed by hand from the electrodes 51 or are automatically removed by any suitable device. The particles having heavier characteristics remain within the tank.

To further improve the rapid and accurate transfer of particles having the selected characteristic to the collector electrodes 51, the particles within the tank 1 are agitated either manually or through the use of suitable mechanical means. Such agitation assists the fiuidizing action of the compressed air and enables the realization of an extremely efficient separation of particles.

According to the modification shown in FIGURE 6, the side electrodes comprise a series of elongated electrically conductive rods 61. These rods are in parallel relationship with each other and are arranged in two groups which extend laterally from opposite sides of the tank 1. The axes of the rods 61 extend in a horizontal plane which is at the level of the upper periphery of the tank. The rods are electrically connected to ground, while the particles 2 within the tank are at a high negative potential. The selected particles are collected by the rods in the manner described above and are discharged into a suitable receiving device (not shown in FIG. 6). Instead of the rods 61, a large mesh grid, for example, may be arranged in a like manner.

In some good arrangements, the side electrodes extend in vertical planes adjacent opposite sides of the fluidized bed of particles. In the FIGURE 7 embodiment, for example, there is provided a pair of vertically extending plates 71 of electrically conductive material which are disposed above the fiuidizing tank 1 and are laterally spaced therefrom. In other advantageous embodiments, the electrodes are inclined in the manner shown by the plates 81 in FIGURE 8. The plates 81 are disposed in planes which converge above the fluidized bed such that the selected particles contacting the plates move downwardly along their surfaces and are received outside the tank 1 by a suitable container (not shown).

It Will be noted that in each of the foregoing embodiments the charging electrode within the fluidized bed not only effects the electrical charging of the particles to be sorted but also establishes the electrical extractor field between the charging electrode and the external collector electrode. The charging electrode may be of any suitable form, in addition to the form shown, and illustratively may comprise horizontal rods or a network of points. It may also be formed by the porous wall 3 (FIGURE 1), in which case the wall is of electrically conductive material.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. A method for the electrostatic sorting of particles having particular characteristics, comprising the steps of forming a fluidized bed of the particles to be sorted, electrically charging the particles in said fluidized bed to a DC. potential of the same polarity, forming an electrostatic extracting field between an electrode immersed in said fluidized bed and a collector member in spaced relationship with said bed, at least some of the charged particles being withdrawn out of said bed and into contact with said collector member substantially solely by said electrostatic extracting field, electrostatically retaining on said collector member only those particles having a common characteristic different from the corresponding characteristic of the remaining particles, and thereafter removing the retained particles from said collector member.

2. A method for the electrostatic sorting of particles having particular characteristics, comprising the steps of forming a fluidized bed of the particles to be sorted, electrically charging the particles in said fluidized bed to a DO potential of the same polarity, continuously advancing a conveyor member along a feed path in spaced juxtaposed relationship with said fluidized bed, forming a vertically extending electrostatic extracting field within said fluidized bed, at least some of the charged particles being withdrawn out of said bed and into contact with said conveyor member substantially solely by said electrostatic extracting field, the electrostatic attraction between said particles and said conveyor member being suflicient to retain thereon only those particles having a common characteristic different from the corresponding characteristic of the remaining particles, and thereafter removing the retained particles from said conveyor member at a collecting station disposed along said feed path.

3. A method for the electrostatic sorting of particles having different resistivity characteristics, comprising the steps of forming a fluidized bed of the particles to be sorted, electrically charging the particles in said fluidized bed to a high DC. potential of the same polarity, forming an electrostatic extracting field between an electrode immersed in said fluidized bed and a collector member in spaced relationship with said bed, substantially all of the charged particles being withdrawn out of said bed and into contact with said collector member substantially solely by said electrostatic extracting field, electrostatically retaining on said collector member only those particles having a comparatively high resistivity characteristic, when compared with the resistivity characteristic of the remaining particles, and thereafter removing the retained particles from said collector member.

4. A method for the electrostatic sorting of particles having varied granulometry characteristics, comprising the steps of forming a fluidized bed of the particles to be sorted, electrically charging the particles in said fluidized bed to a DC. potential of the same polarity, forming an electrostatic extracting field between an electrode immersed in said fluidized bed and a collector member in spaced relationship with said bed, at least some of the charged particles being withdrawn out of said bed and into contact with said collector member substantially solely by said electrostatic extracting field, the strength of said field being such that only those particles having a comparatively light weight characteristic are transfered to said collector member, and thereafter removing the particles transferred to said collector member,

5. A method for the electrostatic sorting of particles having particular characteristics, comprising the steps of forming a fluidized bed of the particles to be sorted, said fluidized bed having an observable free upper surface, connecting a high DC. voltage source across a charging electrode within said fluidized bed and a collector member in spaced relationship therewith, to electrically charge substantially all of the particles in said bed to a DC. potential of the same polarity, said voltage source forming an electrostatic extracting field between said charging electrode and said collector member, at least some of the charged particles being withdrawn upwardly above said upper surface and into contact with said collector member substantially solely by said electrostatic extracting field, electrostatically retaining on said collector member only those particles having a common characteristic different from the cor-responding characteristic of the remaining particles, and thereafter removing the retained particles from said collector member.

6. A method for the electrostatic sorting of particles having different resistivity characteristics, comprising the steps of forming a fluidized bed of the particles to be sorted, said fluidized bed having an observable free upper surface, electrically charging substantially all of the particles in said fluidized bed to a high DC. potential of the same polarity, continuously advancing a conveyor member of electrically conductive material along a feed path in spaced juxtaposed relationship with the upper surface of said fluidized bed, forming a vertically extending electrostatic extracting field between an electrode immersed in said fluidized bed and said conveyor member, substantially all of the charged particles being withdrawn upwardly above said upper surface and into contact with said collector member substantially solely by said electrostatic extracting field, electrostatically retaining on said conveyor member only those particles having a substantially non-conductive characteristic, the charge on the electrically conductive particles being dissipated as they contact said conveyor member to enable the return of said electrically conductive particles to said fluidized bed, and thereafter removing the substantially non-conductive particles from said conveyor member at a collecting station disposed along said feed path.

7. In apparatus for the electrostatic sorting of particles having particular characteristics, a container for the particles to be sorted, said container including a bottom portion and side walls extending upwardly from said bottom portion, means for directing a stream of fluidizing gas into said container to form a fluidized bed of said particles, a collector member in spaced juxtaposed relationship with said container, and means including a charging electrode disposed within said fluidized bed and spaced above the bottom portion of said container for applying a DC. potential of the same polarity to the particles in said container and for forming an electrostatic extracting field between said charging electrode and said collector member, at least some of the charged particles being withdrawn out of said bed and into contact with said collector member substantially solely by said electrostatic extracting field, the electrostatic attraction between said particles and said collector member being suflicient to retain thereon only those particles having a common characteristic different from the corresponding characteristic of the remaining particles.

8. Apparatus for the electrostatic sorting of particles having particular characteristics, comprising a container for the particles to be sorted, said container having side walls and an open top, means for forming a fluidized bed of the particles in said container, a collector member in spaced juxtaposed relationship with the open top of said container, charging means for applying a high D.C. potential of the same polarity to substantially all of the particles in said container and for forming a vertically extending electrostatic extracting field between said charging means and said collector member, at least some of the charged particles being withdrawn upwardly out of the open top of said container and into contact with said collector member substantially solely by said electrostatic extracting field, the electrostatic attraction between said particles and said collector member being sufficient to retain thereon only those particles having a common characteristic different from the corresponding characteristic of the remaining particles, and means for thereafter removing the retained particles from said collector member.

9. Apparatus for the electrostatic sorting of particles having particular characteristics, comprising a container for the particles to be sorted, said container having side walls and an open top, means for forming a fluidized bed of the particles in said container, said fluidized bed having an observable free upper surface, a conveyor member disposed adjacent the open top of said container, means for continuously advancing said conveyor member along a feed path in spaced juxtaposed relationship with said fluidized bed, charging means for applying a high DC. potential of the same polarity to the particles in said container and for forming a vertically extending electrostatic extracting field within said container, said extracting field extending upwardly above the open top of said container to said conveyor member, at least some of the charged particles being withdrawn upwardly above said upper surface and out of said open top into contact with said conveyor member substantially solely by said electrostatic extracting field, the electrostatic attraction between said particles and said conveyor member being sufiicient to retain thereon only those particles having a common characteristic different from the corresponding characteristic of the remaining particles, and means positioned along said feed path for thereafter removing the retained particles from said conveyor member.

10. Apparatus for the electrostatic sorting of particles having different resistivity characteristics, comprising a container for the particles to be sorted, said container including a bottom portion and side walls extending upwardly from said bottom portion, means for forming a fluidized bed of the particles in said container, a conveyor member of electrically conductive material disposed adjacent said container, means for continuously advancing said conveyor member along a feed path in spaced juxtaposed relationship with said fluidized bed, means including a charging electrode within said fluidized bed for applying a high DC potential of the same polarity to the particles in said container and for forming an electrostatic extracting field between said charging electrode and said collector member, said charging electrode being spaced above the bottom portion of said container, substantially all of the charged particles being withdrawn upwardly above said upper surface and out of said open top into contact with said conveyor member substantially solely by said electrostatic extracting field, the electrostatic attraction between said particles and said conveyor member being suflicient to retain thereon only those particles having a comparatively high resistivity characteristic, when compared with the resistivity characteristic of the remaining particles, and means positioned along said feed path for thereafter removing the retained particles from said conveyor member.

11. Apparatus for the electrostatic sorting of particles having particular characteristics, comprising a container for the particles to be sorted, said container having side walls and an open top, a charging electrode disposed within said container, means for forming a fluidized bed of the particles in said container, collector means in spaced juxtaposed relationship with the open top of said container and including an auxiliary electrode, a source of high DC. potential, means for connecting said source across said charging electrode and said auxiliary electrode to electrostatically charge the particles in said container to the same polarity, at least some of the charged particles being withdrawn upwardly out of the open top of said container and into contact with said collector means substantially solely by the electrostatic field formed by said source, but the electrostatic attraction between said particles and said collector means being suflicient to retain thereon only those particles having a common characteristic dilferent from the corresponding characteristic of the remaining particles, and means for thereafter removing the retained particles from said collector means.

12. Apparatus of the character set forth in claim 11, in which said collector means includes an elongated conveyor belt having a collecting surface disposed between said fluidized bed and said auxiliary electrode.

13. Apparatus of the character set forth in claim 11, in which said collector means includes an elongated conveyor belt having a collecting surface thereon, said auxiliary electrode being interposed between said collecting surface and said fluidized bed.

14. In apparatus for the electrostatic sorting of particles having particular characteristics, a container for the parti cles to be sorted, said container having side walls and an open top, means for fluidizing the particles in said container, collector means in spaced juxtaposed relationship with said container, said collector means including a deflector member of generally zig-zag cross-section and a plurality of spaced-apart receiving tanks intermediate said deflector member and said container, and charging means including an electrode for applying a D.C. potential of the same polarity to substantially all of the particles in said container and for forming an electrostatic extracting field between said electrode and said collector means, a portion of the charged particles being withdrawn upwardly out of the open top of said container and being transferred to said collector means substantially solely by said electrostatic extracting field, the particles transferred to said collector means passing between said receiving tanks and being returned thereto by said deflector means, said transferred particles having a common characteristic different from the corresponding characteristic of the remaining particles.

15. In apparatus for the electrostatic sorting of particles having particular characteristics, a container for the particles to be sorted, said container having side walls and an open top, means for fluidizing the particles in said container, means including a collector electrode positioned to one side of said container in spaced juxtaposed relationship therewith, and charging means including a charging electrode within said container and a high DC. voltage source having one terminal electrically connected to said collector electrode and the other terminal electrically connected to said charging electrode for appying a DC. potential of the same polarity to said particles, said charging means forming an electrostatic extracting field between said charging electrode and said collector electrode, a portion of the charged particles being withdrawn upwardly out of the open top of said container and being transferred to said collector electrode substantially solely by said electrostatic extracting field, the particles transferred to said collector electrode having a common characteristic different from the corresponding characteristic of the remaining particles.

16. Apparatus of the character set forth in claim 15, in which a plurality of said collector electrodes is positioned adjacent opposite sides of said container, each of said collector electrodes comprising an elongated horizontally extending rod of electrically conductive material.

17. In apparatus for the electrostatic sorting of particles having particular characteristics, a container for the particles to be sorted, said container having side walls and an open top, means for fluidizing the particles in said container, collector means including a plurality of substantially flat plates disposed about the periphery of said container in spaced juxtaposed relationship therewith, and charging means including a charging electrode within said container and a high DC. voltage source having one terminal electrically connected to said electrically connected to said charging electrode for applying a DC. potential of the same polarity to said particles, said charging means forming an electrostatic extracting field between said charging electrode and said plates, a portion of the charged particles being withdrawn upwardly out of the open top of said container and being transferred to said plates substantially solely by said electrostatic extracting field, the particles transferred to said plate having a common characteristic different from the corresponding characteristic of the remaining particles.

18. Apparatus of the character set forth in claim 17, in which said plates are disposed in a single horizontal plane above the level of the fluidized particles within said container.

19. Apparatus of the character set forth in claim 17, in which the planes of said plates are inclined in converging relationship with each other.

References Cited UNITED STATES PATENTS 880,891 3/1908 Lawson 209--128 2,116,613 5/1938 Bedford 209131 2,300,324 10/ 1942 Thompson 209127 2,786,635 3/1957 Oishi '209-127 2,889,042 6/1959 Le Baron 209-l27 2,899,055 8/1959 Le Baron 209-127 FOREIGN PATENTS 143,744 4/1962 U.S.S.R.

FRANK W. LUTTER, Primary Examiner. 

1. A METHOD FOR THE ELECTROSTATIC SORTING OF PARTICLES HAVING PARTICULAR CHARACERISTICS, COMPRISING THE STEPS OF FORMING A FLUIDIZED BED OF THE PARTICLES TO BE SORTED, ELECTRICALLY CHARGING THE PARTICLES IN SAID FLUIDIZED BED TO A D.C. POTENTIAL OF THE SAME POLARITY, FORMING AN ELECTROSTATIC EXTRACTING FIELD BETWEEN AN ELECTRODE IMMERSED IN SAID FLUIDIZED BED AND A COLLECTOR MEMBER IN SPACED RELATIONSHIP WITH SAID BED, AT LEAST SOME OF THE CHARGED PARTICLES BEING WITHDRAWN OUT OF SAID BED AND INTO CONTACT WITH SAID COLLECTOR MEMBER SUBSTANTIALLY SOLELY BY SAID ELECTROSTATIC EXTRACTING FIELD, ELECTROSTATICALLY RETAINING ON SAID COLLECTOR MEMBER ONLY THOSE PARTICLES HAVING A COMMON CHARACTERISTIC DIFFERENT FROM THE CORRESPONDING CHARACTERISTIC OF THE REMAINING PARTICLES, AND THEREAFTER REMOVING THE RETAINED PARTICLES FROM SAID COLLECTOR MEMBER.
 7. IN APPARATUS FOR THE ELECTROSTATIC SORTING OF PARTICLES HAVING PARTICULAR CHARACTERISTICS, A CONTAINER FOR THE PARTICLES TO BE SORTED, SAID CONTAINER INCLUDING A BOTTOM PORTION AND SIDE WALLS EXTENDING UPWARDLY FROM SAID BOTTOM PORTION, MEANS FOR DIRECTING A STREAM OF FLUIDIZING GAS INTO SAID CONTAINER TO FORM A FLUIDIZED BED OF SAID PARTICLES, A COLLECTOR MEMBER IN SPACED JUXTAPOSED RELATIONSHIP WITH SAID CONTAINER, AND MEANS INCLUDING A CHARGING ELECTRODE DISPOSED WITHIN SAID FLUIDIZED BED AND SPACED ABOVE THE BOTTOM PORTION OF SAID CONTAINER FOR APPLYING A D.C. POTENTIAL OF THE SAME POLARITY TO THE PARTICLES IN SAID CONTAINER AND FOR FORMING AN ELECTROSTATIC EXTRACTING FIELD BETWEEN SAID CHARGING ELECTRODE AND SAID COLLECTOR MEMBER, AT LEAST SOME OF THE CHARGED PARTICLES BEING WITHDRAWN OUT OF SAID BED AND INTO CONTACT WITH SAID COLLECTOR MEMBER SUBSTANTIALLY SOLELY BY SAID ELECTROSTATIC EXTRACTING FIELD, THE ELECTROSTATIC ATTRACTION BETWEEN SAID PARTICLES AND SAID COLLECTOR MEMBER BEING SUFFICIENT TO RETAIN THEREON ONLY THOSE PARTICLES HAVING A COMMON CHARACTERISTIC DIFFERENT FROM THE CORRESPONDING CHARACTERISTIC OF THE REMAINING PARTICLES. 